Subject: Re: [PATCH v2 06/12] mm/execmem: introduce execmem_data_alloc()

From: Mike Rapoport <[email-masked]>
Date: Sat, 17 Jun 2023 09:51:11 +0300

On Fri, Jun 16, 2023 at 01:01:08PM -0700, Song Liu wrote:
> On Fri, Jun 16, 2023 at 1:51 AM Mike Rapoport <[email-masked]> wrote:
> >
> > From: "Mike Rapoport (IBM)" <[email-masked]>
> >
> > Data related to code allocations, such as module data section, need to
> > comply with architecture constraints for its placement and its
> > allocation right now was done using execmem_text_alloc().
> >
> > Create a dedicated API for allocating data related to code allocations
> > and allow architectures to define address ranges for data allocations.
> >
> > Since currently this is only relevant for powerpc variants that use the
> > VMALLOC address space for module data allocations, automatically reuse
> > address ranges defined for text unless address range for data is
> > explicitly defined by an architecture.
> >
> > With separation of code and data allocations, data sections of the
> > modules are now mapped as PAGE_KERNEL rather than PAGE_KERNEL_EXEC which
> > was a default on many architectures.
> >
> > Signed-off-by: Mike Rapoport (IBM) <[email-masked]>
> [...]
> >  static void free_mod_mem(struct module *mod)
> > diff --git a/mm/execmem.c b/mm/execmem.c
> > index a67acd75ffef..f7bf496ad4c3 100644
> > --- a/mm/execmem.c
> > +++ b/mm/execmem.c
> > @@ -63,6 +63,20 @@ void *execmem_text_alloc(size_t size)
> >                              fallback_start, fallback_end, kasan);
> >  }
> >
> > +void *execmem_data_alloc(size_t size)
> > +{
> > +       unsigned long start = execmem_params.modules.data.start;
> > +       unsigned long end = execmem_params.modules.data.end;
> > +       pgprot_t pgprot = execmem_params.modules.data.pgprot;
> > +       unsigned int align = execmem_params.modules.data.alignment;
> > +       unsigned long fallback_start = execmem_params.modules.data.fallback_start;
> > +       unsigned long fallback_end = execmem_params.modules.data.fallback_end;
> > +       bool kasan = execmem_params.modules.flags & EXECMEM_KASAN_SHADOW;
> > +
> > +       return execmem_alloc(size, start, end, align, pgprot,
> > +                            fallback_start, fallback_end, kasan);
> > +}
> > +
> >  void execmem_free(void *ptr)
> >  {
> >         /*
> > @@ -101,6 +115,28 @@ static bool execmem_validate_params(struct execmem_params *p)
> >         return true;
> >  }
> >
> > +static void execmem_init_missing(struct execmem_params *p)
> 
> Shall we call this execmem_default_init_data?

This also fills in jit.text (next patch), so _data doesn't work here :)
And it's not really a default, the defaults are set explicitly for arches
that don't have execmem_arch_params.
 
> > +{
> > +       struct execmem_modules_range *m = &p->modules;
> > +
> > +       if (!pgprot_val(execmem_params.modules.data.pgprot))
> > +               execmem_params.modules.data.pgprot = PAGE_KERNEL;
> 
> Do we really need to check each of these? IOW, can we do:
> 
> if (!pgprot_val(execmem_params.modules.data.pgprot)) {
>        execmem_params.modules.data.pgprot = PAGE_KERNEL;
>        execmem_params.modules.data.alignment = m->text.alignment;
>        execmem_params.modules.data.start = m->text.start;
>        execmem_params.modules.data.end = m->text.end;
>        execmem_params.modules.data.fallback_start = m->text.fallback_start;
>       execmem_params.modules.data.fallback_end = m->text.fallback_end;
> }

Yes, we can have a single check here.
 
> Thanks,
> Song
> [...]

-- 
Sincerely yours,
Mike.